In liquid developed electrophotocopiers, the developer comprises toner particles suspended in a dielectric carrier or dispersant liquid. Latent images formed on a photoconductive surface are developed by contact with the liquid developer. The charged toner particles are attracted to the latent image; and the entire photoconductive surface is wetted by the carrier or dispersant. The developed image on the photoconductive surface is usually subjected to the action of a closely spaced reverse roller which reduces to a minimum the thickness of the layer of carrier liquid on the drum surface. When a copy sheet is brought into contact with the drum surface and the image transferred to the copy sheet, the entire copy sheet is slightly wetted or dampened by the dispersant carrier liquid. The copy sheet is then heated, not only to vaporize the carrier liquid in non-image areas, but also to fix the developed image. In image areas, a small portion of the dispersant carrier may combine with the toner particles; and the residual uncombined carrier must be vaporized.
The drying and fixing of liquid developed electrophotocopier images is usually accomplished by electrical heaters. Normal 120 volt, 15 ampere, electrical service provides an available power of 1800 watts. This amount of power is suitable only for liquid developed electrophotocopiers providing perhaps ten to twenty copies per minute. For electrophotocopiers providing more than thirty copies per minute, a 220 volt high amperage electrical service must be available. Electrophotocopiers employing electrical heaters for drying and fixing typically require at least thirty seconds for the heaters to be brought up to operating temperature. While copies can be produced in a shorter time, such as twenty seconds, the heaters are at too low a temperature; and the initial copy will be faint and poorly fixed.
The vaporized carrier or dispersant, while posing no inherent toxicological hazard, is at least a nuisance; and the room or space in which the electrophotocopier is operated must be adequately ventilated to limit the concentration of dispersant vapor in the air to a reasonably low level. For high speed electrophotocopiers providing more than thirty copies per minute, a hooded exhaust system may have to be installed.
It has been proposed to recycle the carrier vapors and return them in liquid form to the developer supply container of the electrophotocopier. One method of recycling the vaporized carrier is by condensation, which requires bulky and heavy refrigeration equipment providing a sufficiently low temperature to condense an appreciable portion of the vaporized dispersant. Another method is to pass the vapors through an activated charcoal filter for subsequent collection in liquid form.